1. Field of the invention
This invention relates to a charge transfer device such as a charge coupled device imager, and more particularly to a charge transfer device with meander channel.
2. Description of the Prior Art
In solid-state image pickup devices such as CCD imagers, there are ordinarily included light receiving areas arranged in a matrix manner. Signal charges generated in these light receiving areas are transferred to the horizontal register per each line through the vertical registers, and output signals are provided from the horizontal register through the output section.
Meanwhile, with the recent advancement of the imaging technology, realization of the high picture quality, the noninterlace of the monitor picture, and the like are being developed. In CCD imagers, a system of increasing the number of light receiving areas in a horizontal direction to provide a high horizontal resolution, and an entire pixel readout system, etc. are being studied.
For example, in the case of carrying out a readout by the entire pixel readout system, when a structure of a single horizontal register is employed, such a horizontal register must be driven by a clock frequency twice higher that of an ordinary interlace system. As a result, that transfer cannot be satisfactorily carried out.
To overcome this, there is known a technology in which a plurality of, such as, for example, two or three horizontal registers are employed. By increasing the number of horizontal registers, it is possible to reduce a clock frequency for drive.
Generally, the horizontal register has a structure in which a large number of transfer electrodes are arranged in a transfer direction on the gate insulating film.
However, when the horizontal resolution of a CCD imager including a horizontal register of such a structure is caused to be high, the pitch in a horizontal direction becomes narrow, so the transfer electrodes on the horizontal register are formed as a pattern short in a horizontal direction and long in a vertical direction. Further, since transfer between horizontal registers is carried out in a vertical direction which is the longitudinal direction of the pattern, a fringing electric field is difficult to be produced in the vertical direction. For this reason, transfer between horizontal registers cannot be efficiently carried out.
As the technology prior to this application, as described in the publication of the Japanese Patent Application Laid Open (KOKAI) No. 78572/84, there is known a CCD of so called a meander channel type in which the charge transfer path is formed as a zigzag pattern. The CCD of the meander channel type permits employment of a broad pitch width corresponding to one bit with respect to realization of high horizontal resolution, but does not refer by any means to the efficiency of transfer between horizontal registers as the point at issue.